A. Field of the Invention
The invention generally concerns the use of materials such as greenhouse films or sheets that are capable converting light into a more acceptable form for agricultural and plant growing purposes. In particular, the materials include organic fluorescent dyes or combinations of such dyes (e.g., perylene and/or perinone compounds) that are solubilized within a polymeric matrix, where the polymeric matrix containing the solubilized fluorescent dye is capable of absorbing light comprising a wavelength of 500 to 700 nm and emitting the absorbed light at a wavelength of greater than 550 to 800 nm.
B. Description of Related Art
Plants rely on light within the Photosynthetically Active Radiation (PAR) region as a source of energy for photosynthesis. The PAR region is typical referred to as light or radiation having a wavelength between 400 to 700 nanometers. Of this, light having a wavelength of about 400 to 500 nanometers (or blue light) and 600 to 700 nanometers (or red light) are more efficiently used by plants in the photosynthesis process. Red light is also known to promote plant germination and rooting. By comparison, light having a wavelength between about 500 to 600 nanometers (or green/yellow light) is not efficiently used by plants. Further, light having a wavelength of about 700 to 800 nanometers (or far-red light) promotes petiole elongation while inhibiting germination and rooting in plants.
There have been several attempts to positively impact plant growth by manipulating the amount of red to far-red light (“Red to Far-Red Ratio” or “R:FR”) that a plant receives. Increasing the R:FR can increase plant growth and quality, whereas decreasing the R:FR ratio can decrease plant growth and quality. These attempts typically involve the use of greenhouse materials that are designed to manipulate natural sunlight passing through the materials. One of the more prevalent strategies is to selectively absorb light in one of the two red regions with pigments—pigments can absorb certain light and reflect others but are inefficient at converting light from one wavelength to another. For example, absorbing far-red light more than red-light leads to an increase in the Red/Far-Red ratio.
Other strategies attempt to increase the transmittance of the more important light ranges from 400 to 500 nm or 600 to 700 nm, while simultaneously reflecting the least important range of 500 to 600 nm (see U.S. Pat. No. 4,529,269). The goal of such a strategy is to simply focus on the growth important light and ignore the remaining “unimportant light.”
Problems associated with the current greenhouse materials are at least three-fold. First, several of the compounds and pigments used are not sufficiently stable from either a photo or thermal stability perspective. This is problematic given that greenhouse materials are typically subjected to prolonged outdoor use. Second, pigments are insoluble particles and have a tendency to coalesce together, which can create uneven distribution into a given material, thereby negatively affecting the efficacy of the material (e.g., some portions of the material may not have pigments or an insufficient amount to perform the desired result). Further, their insolubility limits the amount that can be used in a given material. Third, current strategies do not efficiently modify the R:FR ratio. Either several different types of ingredients are typically used to achieve an acceptable ratio or the strategies appear to be limited to the amount of red/far red light present in natural sunlight.